High temperature organic/inorganic addition cure polyimide composites, part 1: Matrix thermal properties

Carborane-Containing Aromatic Polyimide Films with Ultrahigh Thermo-Oxidative Stability

Carborane-containing aromatic polyimide (CPI) films with ultrahigh thermo-oxidative stability at 700 °C have been prepared by casting poly(amic acid) (PAA) resin solution on a glass surface, followed by thermal imidization at elevated temperatures. The PAA solution was prepared by copolymerization of an aromatic dianhydride and an aromatic diamine mixture, including carborane-containing aromatic diamine in an aprotic solvent. The CPI films showed excellent thermo-oxidative stability at 700 °C due to the multilayered protection layers formed on the film surface by thermal conversion of the carborane group into boron oxides. The boron oxide layer enhanced the degradation activation energy and suppressed the direct contact of inner polymer materials with oxygen molecules in a high-temperature environment, acting as a “self-healing” skin layer on the polyimide materials. The CPI-50 film was still flexible and maintained 50% retention of mechanical strength even after thermo-oxidative aging at 700 °C/5 min. The mechanism of thermo-oxidative degradation was proposed.

Phenylethynyl-terminated oligoimides based on bis(p-aminophenoxy)dimethyl silane: Effect of siloxane structure on processability and thermal stability

A series of phenylethynyl-terminated oligoimides based on 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA), 2,2′-bis(trifluoromethyl)benzidine (TFDB), and bis( p-aminophenoxy)dimethyl silane (APDS) with different siloxane content and various calculated molecular weights were synthesized. The effect of siloxane structure on the processability of oligoimides and the thermal stability of cured polyimides (PIs) was investigated. The results indicated that the oligoimides have lower melt viscosity and broader processing window with the incorporation of flexible siloxane segment. The thermal stability of the cured PIs can be significantly enhanced by high-temperature postcuring due to the oxidative cross-linking of siloxane. The polyimide PI-s1-15 exhibited good balance between processability and thermal stability with the minimum melt viscosity of 0.4 Pa·s at 325°C and glass transition temperature as high as 470°C after postcuring at 450°C. The carbon fiber-reinforced composite T800/PI-s1-15 displayed excellent high-temperature performance, which gave the flexural strength and interlaminar shear strength of 703 and 33 MPa, respectively, when tested at the temperature as high as 450°C.

Thermal curing of novel carborane-containing phenylethynyl terminated imide oligomers

The thermal behavior of novel carborane-containing phenylethynyl terminated imide model compound and resultant resin systems was studied in this paper.